Apparatus and method for coating discrete solids



May 30, 1961 H. w. MESNARD ETAL 2,986,475

APPARATUS AND METHOD FOR comma DISCRETE SOLIDS Filed Nov. 5, 1958 INVENTORS 38 HOWARD W.MESNARD,

EARL ROSEN a MORTON w. SCOTT ATTORNEYS APPARATUS AND METHOD FOR COATING DECRETE SOLIDS Howard W. Mesnard, Devon, and Earl Rosen and Morton W. Scott, Philadelphia, Pa., assignors to Smith, Kline & French Laboratories, Philadelphia, Pa., a corporation of Pennsylvania Filed Nov. 5, H56, Ser. No. 772,103

18 Claims. (Cl. 117-100) This invention relates to apparatus and a method for coating discrete solids, for example, with a liquid containing a coating material or with an adhesive liquid and then a powder. Typical applications are the coating of particles such as sugar seeds, sometimes referred to as nonpareils seeds, or tablets, or pellets with, for example, coating materials in organic solvents or an adhesive liquid followed by a powdered material. A major utility is in forming discrete solids coated with a medicament and/or a time delay material such as a wax.

It is therefore an object of this invention to provide apparatus and a method for coating discrete solids.

It is a further object of this invention to provide apparatus and a method for coating discrete solids in which the discrete solids, during the coating operation, are suspended in a gas.

It is a still further object of this invention to provide apparatus and a method for coating discrete solids in which the solids are suspended in a gas and coating material is delivered in a direction opposite to the direction of movement of the particles to be coated.

It is an additional object of this invention to provide apparatus and a method for coating in which the solids to be coated are suspended in a gas and which do not require frequent regulation of the rate of flow of the gas to keep the solids in suspension as their weight increases incident to the application of the coating material.

It is an additional object of this invention to provide apparatus and method for coating discrete solids in which an exceptionally large weight of solids can be suspended within a given cross-sectional area.

It is an additional object of this invention to provide apparatus for coating particles in which more than one coating can be applied to the particles during the same coating operation.

These and other objects of this invention will become apparent on reading the following description in conjunction with the drawings in which:

Figure l is a front elevation partially broken away of apparatus in accordance with this invention; and

Figure 2 is a vertical section partially broken away and taken on the plane indicated by the line 22 in Figure 1.

As shown in Figure l, apparatus 2, in accordance with this invention, is provided with a coating chamber 4 having a body portion 6, a truncated lower portion 8 and a truncated upper portion 10. Truncated portion 8 is flanged at 14 to an air supply line 12 which is substantially smaller in cross-sectional area than body portion 6 and line 12 in turn is flanged to line 16 as shown at 18.

Advantageously, the cross-sectional area of the body portion 6 will be from about 4 to about 100 times, preferably from about 6 to about 15 times, the crosssectional area of the air supply line 12. Line 16 is secured to the top of a chamber 20 and has its lower end secured to a bell-shaped conduit 22 lying within chamber 2,986,475 Patented May 30, 1961 20. A conduit 24 is connected to chamber 20 and has a reduced inlet portion connected to the discharged side of blower 28. Steam coils 29 pass through conduit 24 to heat the air when desired. Blower 28 is driven by a conventional variable speed belt drive 30 which in turn is driven by a motor 32.

Chamber 20 is provided with a hinge access door 34 and a drawer type recovery pan 36 which is carried on runners 38 mounted within chamber 20.

Atomized coating material is supplied to the interior of chamber 4 by means of upwardly directed atomizing nozzle 44 which is secured to lower portion 8 of chamber 6. Nozzle 44 is connected to jacketed line 46 which in turn is connected to the discharge side of pump 48. The intake side of pump 48 is connected to a jacketed line 50 which is connected to a reservoir 52 which contains coating material 54. A line 58 is connected to valve 44 and supplies air under pressure to nozzle 44. A steam heating coil 56 is provided to heat the coating material 54 when it is not a liquid at room temperature.

The upper portion 10 of chamber 4 is connected to an exhaust line 62 which is flanged to a reduced portion 64 discharging into a centrifugal separator 66. Separator 66 is connected to a gas exhaust line 68 and discharges the separated solids through its lower end 69 into a container indicated at 70.

For the introduction of the discrete solids to be coated there is provided a hopper 74 having its discharge end connected to a rubber sleeve 76 containing a pinch valve 78. Sleeve 76 is connected to line 79 which discharges into line 62. The upper portion of hopper 74 has a removable cap 80.

For the introduction of solid coating material there is provided a line 82 connected to line 16 and supplied with air under pressure from a source not shown. Line 82 has a venturi portion 84 to which is connected a supply hopper 86.

A downwardly directed atomizing nozzle passes through portion 10 of chamber 4 and is adapted to direct a coating material at the solids in the upper portion of chamber 4. A coating material supply line 92 and an air supply line 94 are connected to nozzle 90.

Operation When it is desired to coat discrete solids with a liquid coating material, the operation is initiated by starting up motor 32 to drive blower 28 and hence cause a flow of air through the apparatus 4. With valve 78 in the open position, the discrete solids to be coated flow downwardly through sleeve 76, into line 62 and thence into chamber 4. The rate of flow of air is adjusted so that the solids will remain suspended in the air within chamber 4 without dropping down through line 12 or being exhausted through line 62. By employing a diameter for body 6 substantially larger than that of line 12, the velocity of the air as it enters chamber 4 is suflicient to force the contained solids upwardly through the center of the chamber. In the upper part of chamber 4 the velocity due to the greater cross-section has dropped sufiiciently to permit the solids to drop downwardly along the outer periphery of the chamber. Satisfactory operation is achieved at a given rate of air flow 'for solids of a wide range of size and weight.

Pump 48 is now started to supply the liquified coating material 54 from reservoir 52 through lines 50 and 46 to the nozzle 44. At the same time air is supplied to nozzle 44 through line 58 to provide for the atomization of the coating material 54. Nozzle 44 thus introduces upwardly to chamber 4 the atomized coating material 54. The nozzle is so directed that the atomized coating material in the greatest concentration engages the solids within chamber 4 as they are falling.

The coating is continued until the solids have been coated to the desired weight of coating, at which time the air in line 58 and pump 48 are shut off. Subsequently, the flow of air through the apparatus is discontinued by shutting off motor $2. With no air flow to support them, the solids in chamber 4 fall downwardly through lines 12 and 16 into chamber 2% where they are collected in pan 36.

If it is desired to cover discrete solids with a powder, this is accomplished by operating the apparatus 2 in a manner very similar to that described above. The only deviation is that in lieu of the coating material 54 there is employed a liquid adhesive material. Simultaneously, with the atomization of the adhesive material through nozzle 44, coating powder is introduced into hopper 86, is drawn into venturi 84, through lines '82, 16 and 12 into chamber 4 where, being well distributed throughout the air, it will coat the solids circulating within chamber 4.

Again, if desired, after a coating material has been applied by nozzle 44, a different coating material can be applied by nozzle 90. On the other hand, difi'erent coating materials can be applied by operating nozzles 44 and 90 at the same time.

It will be appreciated that this invention is broadly applicable to the coating of discrete solids with any desired liquid coating material.

What is claimed is:

l. A device for coating discrete solids comprising an upstanding coating chamber, a gas supply line connected to the lower end of the coating chamber and having a cross-sectional area substantially smaller than the crosssectional area of the coating chamber, means to supply a gas under pressure to said line, means to exhaust the gas from the upper end of the coating chamber, means to introduce discrete solids to be coated into said chamber, means to spray an adhesive liquid into said coating chamber to coat the discrete solids and means to introduce a coating powder into the gas supply line to provide for the coating of the discrete solids with said powder, said line and said chamber forming a continuous unobstructed gas passage with the gas flowing through the said line into said chamber adapted to suspend the solids in said chamber and prevent the solids from entering said line due to the resultant greater velocity of gas flow in said line than in said chamber.

2. A device for coating discrete solids comprising an upstanding coating chamber, a gas supply line connected to the lower end of the coating chamber and having a cross-sectional area substantially smaller than the crosssectional area of the coating chamber, means to supply a gas under pressure to said line, said means comprising a gas chamber below said gas supply line and blower means adapted to supply a gas under pressure to said gas chamber, means to exhaust the gas from the upper end of the coating chamber, means to introduce discrete solids to be coated into said chamber, and means to spray a coating liquid into said coating chamber to coat the discrete solids, and a container removably mounted in said gas chamber for the collection of coated discrete solids on cut-01f of the flow of gas to the coating chamber, said line and said chamber forming a continuous unobstructed gas passage with the gas flowing through the said line into said chamber adapted to suspend the solids in said chamber and prevent the solids from entering said line due to the resultant greater velocity of gas flow in said line than in said chamber.

3. A device for coating discrete solids comprising an upstanding coating chamber which is substantially circular in cross-section, a gas supply line connected to the lower end of the coating chamber and having a crossscctional area substantially smaller than the crosssectional area of the coating chamber, a blower connected to said gas supply line to supply a gas under pressure to said line, an exhaust conduit connected to the upper end of said coating chamber, a line connected to said coating chamber for the introduction of discrete solids to be coated into said chamber, a spray nozzle communicating with the interior of said coating chamher to spray a coating liquid into said chamber to coat the discrete solids, and a powder supply conduit communicating with the gas supply line to provide for the coating of the discrete solids with a powder, said gas supply line and said coating chamber being coaxial at their juncture and forming a continuous unobstructed gas passage at their juncture with the gas flowing through the said line into said chamber adapted to suspend and circulate the solids in said chamber and prevent solids from entering said line due to the resultant greater velocity of said gas flow in said line than in said chamher.

4. A device for coating discrete solids comprising an upstanding coating chamber, a gas supply line connected to the lower end of the coating chamber and having a cross-sectional area substantially smaller than the area of the coating chamber, a gas chamber below said gas supply line, a blower adapted to supply a gas under pressure to said gas chamber, an exhaust conduit communicating with the upper end of the coating chamber, a supply conduit communicating with the upper portion of said coating chamber for the introduction of discrete solids to be coated into said chamber, a spray nozzle communicating with the interior of said coating chamber to spray a coating liquid into said chamber to coat the discrete solids and a container rcmovably mounted in said gas chamber for the collection of coated discrete solids on cut-off of the flow of gas to the coating chamber, said line and said chamber forming a continuous unobstructed gas passage at their juncture with the gas flowing through said line into said chamber adapted to suspend and circulate the solids in said chamber and prevent the solids from entering said line due to the resultant greater velocity of gas flow in said line than in said chamber.

5. A device for coating discrete solids comprising an upstanding coating chamber having a body portion and a lower portion, a gas supply line connected to the lower end of said lower portion and having a cross-sectional area substantially smaller than the body portion of the coating chamber, said lower portion tapering from the body portion to its juncture with the gas supply line. means to supply a gas under pressure to said line, means to exhaust the gas from the upper end of the coating chamber, means tointroduce discrete solids to be coated into the coating chamber, means at a location above the juncture of said lower portion of the coating chamber and the gas supply line to spray a coating liquid into the coating chamber to .coat the discrete solids and means to remove the discrete solids from the device after they are coated, the upper portion of said line and said chamber being coaxial and forming a continuous unobstructed gas passage, the gas flowing through the said line into the chamber being adapted to maintain in circulation the solids in said chamber by forcing the solids upwardly through the center of the chamber and permitting them to drop downwardly adjacent the outer periphery of the chamber and being adapted to prevent the solids from entering said line.

6. A device in accordance with claim 5 characterized in that it includes means for controlling the temperature of the gas.

7. A device for coating discrete solids comprising an upstanding coating chamber having a body portion and a lower portion, a gas supply line connected to the lower end of said lower portion and having a cross-sectional area of from about 1% to about 25% of the crosssectional area of the body portion of the coating chamber, said lower portion tapering from the body portion to its juncture with the gas supply line, means to supply a gas under pressure to said line, means to exhaust the "gas from the upper end of the coating chamber, means to introduce discrete solids to be coated into the coating chamber, means at a location above the juncture of said lower portion of the coating chamber and the gas supply line to spray a coating liquid into a portion of the coating chamber to coat the discrete solids and means to remove the discrete solids from the device after they are coated, the upper portion of said line and said chamber being coaxial and forming a continuous unobstructed gas passage, the gas flowing through the said line into the chamber being adapted to maintain in circulation the solids in said chamber by forcing the solids upwardly through the center of the chamber and permitting them to drop downwardly adjacent the outer periphery of the chamber and being adapted to prevent the solids from entering said line.

8. A device for coating discrete solids comprising an upstanding coating chamber having a body portion and a lower portion, a gas supply line connected to the lower end of said lower portion and having a cross-sectional area of from about 1% to about 25% of the cross-sectional area of the body portion of the coating chamber, said lower portion tapering from the body portion to its juncture with the gas supply line, means to supply a gas under pressure to said line, means to exhaust the gas from the upper end of the coating chamber, means to introduce discrete solids to be coated into the coating chamber, means to spray a coating liquid into a portion of the coating chamber in a direction opposite to the direction of flow of said discrete solids to coat the discrete solids and means to remove the discrete solids from the device after they are coated, the upper portion of said line and said chamber being coaxial and forming a continuous unobstructed gas passage, the gas flowing through the said line into the chamber being adapted to maintain in circulation the solids in said chamber by forcing the solids upwardly through the center of the chamber and permitting them to drop downwardly adjacent the outer periphery of the chamber and being adapted to prevent the solids from entering said line.

9. A device for coating discrete solids comprising an upstanding coating chamber having a body portion and a lower portion, a gas supply line connected to the lower end of said lower portion and having a cross-sectional area substantially smaller than the body portion of the coating chamber, said lower portion tapering from the body portion to its juncture with the gas supply line, means to supply a gas under pressure to said line, means to exhaust the gas from the upper end of the coating chamber, means to introduce discrete solids to be coated into the coating chamber, means to spray an adhesive liquid into the coating chamber, means to introduce a coating powder into the gas supply line to provide for the coating of the discrete solids with said powder, and means to remove the discrete solids from the device after they are coated, the upper portion of said line and said chamber being coaxial and forming a continuous unobstructed gas passage, the gas flowing through the said line into the chamber being adapted to maintain in circulation the solids in said chamber by forcing the solids upwardly through the center of the chamber and permitting them to drop downwardly adjacent the outer periphery of the chamber and being adapted to prevent the solids from entering said line.

10. A device for coating discrete solids comprising an upstanding coating chamber having a body portion and a lower portion, a gas supply line connected to the lower end of said lower portion and having a cross-sectional area of from about 1% to about 25% of the crosssectional area of the body portion of the coating chamber, said lower portion tapering from the body portion to its juncture with the gas supply line, means to supply a gas under pressure to said line, means to exhaust the gas from the upper end of the coating chamber, means to introduce discrete solids to be coated into the coating chamber, means to spray an adhesive liquid into the coating chamber, means to introduce a coating powder into the gas supply line to provide for the coating of the discrete solids with said powder, and means to remove the discrete solids from the device after they are coated, the upper portion of said line and said chamber being coaxial and forming a continuous unobstructed gas passage, the gas flowing through the said line into the chamber being adapted to maintain in circulation the solids in said chamber by forcing the solids upwardly through the center of the chamber and permitting them to drop downwardly adjacent the outer periphery of the chamber and being adapted to prevent the solids from entering said line.

11. A device for coating discrete solids comprising an upstanding coating chamber having a body portion and a lower portion, a conduit connected to the lower end of said lower portion and having a cross-sectional area substantially smaller than the body portion of the coating chamber, said lower portion tapering from the body portion to its juncture with said conduit, the upper portion of said conduit and said chamber being coaxial and forming a continuous unobstructed passage, means to introduce a discrete solid to be coated into said chamber, means to spray a coating liquid into said coating chamber to coat the discrete solids, means to flow a gas through said conduit into said chamber to circulate the solids in said chamber by forcing the solids upwardly through the center of the chamber and permitting them to drop downwardly adjacent the outer periphery of the chamber and to prevent the solids from entering said conduit, said gas flow means including means to shut off the flow of gas to permit the solids to drop downwardly through the conduit for collection after the coating.

12. A device for coating discrete solids comprising an upstanding coating chamber having a body portion and a lower portion, a conduit connected to the lower end of said lower portion and having a cross-sectional area of from about 1% to about 25% of the cross-sectional area of the body portion of the coating chamber, said lower portion tapering from the body portion to its juncture with said conduit, the upper portion of said conduit and said chamber being coaxial and forming a continuous unobstructed passage, means to introduce discrete solids to be coated into said chamber, means to spray a coating liquid into the coating chamber to coat the discrete solids, means to flow a gas through said conduit into said chamber to circulate the solids in said chamber by forcing the solids upwardly through the center of the chamber and permitting them to drop downwardly adjacent the outer periphery of the chamber and to prevent the solids from entering said conduit, said gas flow means including means to shut ofi the fiow of gas to permit the solids to drop downwardly through the conduit for collection after the coating.

13. The method of coating discrete solids which comprises introducing a batch of discrete solids into an unobstructed upstanding zone and maintaining said discrete solids incontinuous circulation in said zone, spraying a liquefied coating material into a portion of said zone, said discrete solids being maintained in continuous circulation through the portion of said zone containing the liquefied coating material and through at least part of the remaining portion of said zone to repeatedly apply and solidify the coating material onthe discrete solids and completely coat the discrete solids by maintaining a relatively high velocity gas column below and discharging upwardly without obstruction into the middle of said zone which has a cross-sectional area of from about 4 to about times the cross-sectional area of the gas column below said zone, said gas column carrying the solids upwardly through the middle of said zone with a gradually reducing velocity in the upper portion of said zone to permit them to drop downwardly adjacent the periphery of said zone and by directing said discrete solids back into said gas column when they drop into the lower portion of said zone, the point of introduction of said liquefied coating material being spaced from the point at which the gas column discharges into said zone, exhausting gas from the upper portion of said zone and changing the rate of flow of the gas in said column to remove said batch of coated discrete solids from said zone after the desired amount of coating material has been applied to the discrete solids.

14. The method of claim 13 characterized in that the discrete solids are tablets.

15. The method of claim 13 characterized in that the discrete solids are pellets.

16. The method of claim 13 characterized in that the discrete solids are sugar seeds.

17. The method of claim 13 characterized in that after the desired amount of coating material has been applied to the discrete solids, the How of gas in the column is substantially stopped permitting the batch of discrete solids to drop downwardly below said zone for collection.

18. The method in accordance with claim 13 characterized in that the liquefied coating material is sprayed into said zone in a direction opposite to the direction of flow of said discrete solids.

References Cited in the file of this patent UNITED STATES PATENTS 2,059,983 Dent et al. Nov. 3, 1936 2,586,818 Harms Feb. 26, 1952 2,768,095 Tadema et al. Oct. 23, 1956 2,799,241 Wurster July 16, 1957 

13. THE METHOD OF COATING DISCRETE SOLIDS WHICH COMPRISES INTRODUCING A BATCH OF DISCRETE SOLIDS INTO AN UNOBSTRUCTED UPSTANDING ZONE AND MAINTAINING SAID DISCRETE SOLIDS IN CONTINUOUS CIRCULATION IN SAID ZONE, SPRAYING A LIQUEFIED COATING MATERIAL INTO A PORTION OF SAID ZONE, SAID DISCRETE SOLIDS BEING MAINTAINED IN CONTINUOUS CIRCULATION THROUGH THE PORTION OF SAID ZONE CONTAINING THE LIQUEFIED COATING MATERIAL AND THROUGH AT LEAST PART OF THE REMAINING PORTION OF SAID ZONE TO REPEATEDLY APPLY AND SOLIDFY THE COATING MATERIAL ON THE DISCRETE SOLIDS AND COMPLETELY COAT THE DISCRETE SOLIDS BY MAINTAINING A RELATIVELY HIGH VELOCITY GAS COLUMN BELOW AND DISCHARGING UPWARDLY WITHOUT OBSTRUCTION INTO THE MIDELE OF SAID ZONE WHICH HAS A CROSS-SECTIONAL AREA OF FROM ABOUT 4 TO ABOUT 100 TIMES THE CROSS-SECTIONAL AREA OF FROM ABOUT 4 TO ABOUT LOW SAID ZONE, SAID GAS COLUMN CARRYING THE SOLIDS UPWARDLY THROUGH THE MIDELE OF SAID ZONE WITH A GRADUALLY REDUCING VELOCITY IN THE UPPER PORTION OF SAID ZONE TO PERMIT THEM TO DROP DOWNWARDLY ADJACENT THE PERIPHERY OF SAID ZONE AND BY DIRECTING SAID DISCRETE SOLIDS BACK ONTO SAID GAS COLUMN WHEN THEY DROP INTO THE LOWER PORTION OF SAID ZONE, THE POINT OF INTRODUCTION OF SAID LIQUEFIED COATING MATERIAL BEING SPACED FROM THE POINT AT WHICH THE GAS COLUMN DISCHARGES INTO SAID ZONE, EXHAUSTING GAS FROM THE UPPER PORTION OF SAID ZONE AND CHANGING THE RATE OF FLOW OF THE GAS IN SAID COLUMN TO REMOVE SAID BATCH OF COATED DISCRETE SOLIDS FORM SAID ZONE AFTER THE DESIRED AMOUNT OF COATING MATERIAL HAS BEEN APPLIED TO THE DISCRETE SOLIDS. 